1.Tìm x
a.(\(\frac{3x}{7}\)+1) : (-4) = \(\frac{-1}{28}\)
b.x +30 % x = -1.3
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27 tháng 4 2020
1)a, \(0,5x-\frac{2}{3}x=\frac{7}{12}\) b) \(x:4\frac{1}{3}=-\frac{2}{5}\)
\(x\left(0,5-\frac{2}{3}\right)=\frac{7}{12}\) \(x=-\frac{2}{5}.4\frac{1}{3}\)
\(-\frac{1}{6}x=\frac{7}{12}\) \(x=-\frac{26}{15}\)
\(x=\frac{-7}{2}\)
c) \(\left(\frac{3x}{7}+1\right):\left(-4\right)=-\frac{1}{28}\) d) \(x+30\%x=-1,3\)
\(\frac{3x}{7}+1=-\frac{1}{28}.\left(-4\right)\) \(x\left(1+30\%\right)=-1,3\)
\(\frac{3x}{7}+1=\frac{1}{7}\) \(1,3x=-1,3\)
\(\frac{3x}{7}=-\frac{6}{7}\) \(x=-1,3:1,3\)
\(x=-6.7:7:3\) \(x=-1\)
\(x=-2\)
Bài 2:
\(\frac{3}{5.7}+\frac{3}{7.9}+...+\frac{3}{2019.2021}=\frac{3}{2}\left(\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{2019.2021}\right)\)
\(=\frac{3}{2}\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{2019}-\frac{1}{2021}\right)\)
\(=\frac{3}{2}.\left(\frac{1}{5}-\frac{1}{2021}\right)\)
\(=\frac{3}{2}.\frac{2016}{10105}\)
\(=\frac{3024}{10105}\)
KN
1 tháng 4 2019
a. \(0,5x-\frac{2}{3}x=\frac{7}{12}\)
=>\(\left(0,5-\frac{2}{3}\right).x=\frac{7}{12}\)
=>\(-\frac{1}{6}.x=\frac{7}{12}\)
=>\(x=\frac{7}{12}:-\frac{1}{6}=-\frac{7}{2}\)
_Hok tốt_
KN
1 tháng 4 2019
b.\(x:4\frac{1}{3}=-2,5\)
=>\(x:\frac{13}{3}=-2,5\)
=>\(x=-2,5.\frac{13}{3}=-\frac{65}{6}\)
_Hok tốt_
VN
15 tháng 8 2016
0,5x-2/3x=7/12
=>(1/2-2/3).x=7/12
=>-1/6x=7/12
=>x=7/12:1/6
=>x=7/2
b, x:4 1/3=-2,5
=>x:13/3=-2,5
=>x=-5/2x13/3
=>x=-13
c,5,5x=13/15
=>11/2x=13/15
=>x=13/15:11/2
=>x=26/165
d,(3x/7+1):-4=-1/28
=>3x/7+1=-1/28x(-4)
=>3x/7+1=-1/7
=>3x/7=-1/7-1
=>3x/7=-8/7
=>3x=-8/7x7
=>3x=8
=>x=8:3
=>x=8/3
15 tháng 8 2016
\(0,5x-\frac{2}{3}x=\frac{7}{12}\)
\(\frac{1}{2}x-\frac{2}{3}x=\frac{7}{12}\)
\(\left(\frac{1}{2}-\frac{2}{3}\right)x=\frac{7}{12}\)
\(\frac{-1}{6}x=\frac{7}{12}\)
\(x=-21\)
b,c,d tương tự
12 tháng 7 2018
\(a)\frac{1}{1\cdot3}+\frac{1}{3\cdot5}+...+\frac{1}{x\left(x+2\right)}=\frac{20}{41}\)
\(2\left(\frac{1}{1\cdot3}+\frac{1}{3\cdot5}+...+\frac{1}{x\left(x+2\right)}\right)=2\cdot\frac{20}{41}\)
\(\frac{2}{1\cdot3}+\frac{2}{3\cdot5}+...+\frac{2}{x\left(x+2\right)}=\frac{40}{41}\)
\(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{x}-\frac{1}{x+2}=\frac{40}{41}\)
\(1-\frac{1}{x+2}=\frac{40}{41}\)
\(\frac{x+1}{x+2}=\frac{40}{41}\)
\(\Leftrightarrow\hept{\begin{cases}x+1=40\\x+2=41\end{cases}\Leftrightarrow\hept{\begin{cases}x=40-1\\x=41-2\end{cases}\Leftrightarrow}\hept{\begin{cases}x=39\\x=39\end{cases}}}\)
Vậy x=39
\(b)|x+2016|\ge0\forall x;|x+2017|\ge0\forall x\)
\(\Leftrightarrow x+2016+x+2017+2018=3x\)
\(\Leftrightarrow2x+6051=3x\)
\(\Leftrightarrow6051=3x-2x\)
\(\Leftrightarrow6051=x\)
Vậy x=6051
DD
0
DT
2
19 tháng 5 2015
Loan còn lượt cho đúng cho mình không chứ mấy bn kia chắc ko cho đúng đâu?
22 tháng 3 2017
(3x/7+1):(-4)=-1/28
3x/7+1=-1/28x(-4)
3x/7+1=1/7
3x/7=1/7-1=-6/7
3x=-6
x=-6:3=-2
Vậy x=-2
L
1
30 tháng 3 2016
Chào bạn, bạn hãy theo dõi lời giải của mình nhé!
Ta có :
\(\left(\frac{3x}{7}+1\right):\left(-4\right)=\frac{-1}{28}\)
\(=>\frac{3x}{7}+\frac{7}{7}=\frac{-1}{28}.\left(-4\right)=\frac{-1.\left(-4\right)}{28}=\frac{4}{28}=\frac{1}{7}\)
\(=>\frac{3x+7}{7}=\frac{1}{7}\)
\(=>3x+7=1\)
\(=>3x=1-7=-4\)
\(3x=-4:3=\frac{-4}{3}\)
Chuc bạn học tốt!
17 tháng 4 2019
\(a,2,5\cdot x=\frac{11}{15}\)
\(\Rightarrow x=\frac{11}{15}:2,5\)
\(\Rightarrow x=\frac{11}{15}:\frac{25}{10}\)
\(\Rightarrow x=\frac{11}{15}\cdot\frac{10}{25}\)
\(\Rightarrow x=\frac{11}{3}\cdot\frac{2}{25}=\frac{22}{75}\)
\(b,x-15\%\cdot x=\frac{1}{3}\)
\(\Rightarrow x-\frac{15}{100}\cdot x=\frac{1}{3}\)
\(\Rightarrow x-\frac{3}{20}\cdot x=\frac{1}{3}\)
\(\Rightarrow\frac{20x}{20}-\frac{3x}{20}=\frac{1}{3}\)
\(\Rightarrow\frac{17x}{20}=\frac{1}{3}\)
\(\Rightarrow17x\cdot3=20\)
\(\Rightarrow17x=\frac{20}{3}\)
\(\Rightarrow x=\frac{20}{3}:17=\frac{20}{3}\cdot\frac{1}{17}=\frac{20}{51}\)
Câu c mk làm sau :v
17 tháng 4 2019
c,\(\left[\frac{3x}{7}+1\right]:\left[-4\frac{1}{7}\right]=\frac{-3}{28}\)
\(\Rightarrow\left[\frac{3x}{7}+1\right]:\left[-\frac{29}{7}\right]=\frac{-3}{28}\)
\(\Rightarrow\frac{3x}{7}+1=-\frac{3}{28}\cdot-\frac{29}{7}=\frac{87}{196}\)
\(\Rightarrow\frac{3x}{7}=\frac{87}{196}-1\)
Tìm nốt :v
a) \(\left(\frac{3x}{7}+1\right):\left(-4\right)=\frac{-1}{28}\)
\(\Rightarrow\frac{3}{7}.x+1=\frac{-1}{28}.\left(-4\right)\)
\(\Rightarrow\frac{3}{7}.x=\frac{1}{7}-1\)
\(\Rightarrow\frac{3}{7}.x=\frac{-6}{7}\)
\(\Rightarrow x=\frac{-6}{7}:\frac{3}{7}\)
\(\Rightarrow x=\frac{-6}{7}.\frac{7}{3}\)
\(\Rightarrow x=-2\)
b) x+30%x=-1.3 mình coi 1.3 là 1,3 nhé !
\(\Rightarrow x\left(30\%+1\right)=-1,3\)
\(\Rightarrow x\left(\frac{13}{10}\right)=-\frac{13}{10}\)
\(\Rightarrow x=-\frac{13}{10}:\frac{13}{10}\)
\(\Rightarrow x=-1\)